Comment by grepular

The way your routes work mean that a response is expected to be immediately generated and returned. It would be much nicer if a response object was passed to the callback and you could return immediately from the callback, but send a response independently, when you are ready. Kind of like this:

  CROW_ROUTE(app, "/about")
    ([](Response res){
        res.send("About Crow example");
    });

Why you might ask? So you can do this:

  CROW_ROUTE(app, "/about")
    ([](Response res){
        responses.push_back(res);
    });

And then some independent method could come along and do the res.send() when it is ready. The connection would hang until res.send() or similar is called on it. There would also be methods on the Response object so you can see if the connection is still alive etc, and maybe the ability to set timeouts directly on the Response object.

[edit] This would allow people using your framework to implement long polling without locking up an io_service thread for each connection. It would also make it easier to add support for web sockets etc at a later date.

[edit2] This is how NodeJS works. Both a request and a response object is passed to the callback, then you can do for example:

  function callback (req, res) {
      setTimeout(function(){
          res.writeHead(200, {'Content-Type': 'text/plain'});
          res.end('Hello World\n');
      }, 5000);
  }